Thermal cut-out



June 15 1926. I 1,589,161

J. D. HILLIARD THERMAL CUT-OUT Filed Nov. 1. 1923 member: John D.Hi'lliaa-d,'

His ALLOPheH.

Patented June 15, 1926.

UNITED STATES PATENT OFFICE.

JOHN D. HILLIABD, OE SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

THERMAL CUT-OUT.

Application filed Kovember 1, 1923. Serial No. 672,183.

The present invention relates to protective cut-outs for high potential circuits and more especially to thermal cut-outs of the expulsion type in which a fusible conductor is arranged longitudinally within a discharge barrel so that upon the sudden fusion of the conductor by the passage of excess current the gases evolvedwill be directed lengthwise thereof and blow .out any arc and any unfused portion of the conductor.

The great majority of expulsion cutouts heretofore used for the protection of high potential circuits are of bomb construction with a strong metal explosion chamber and a relatively long and narrow insulating tube extending therefrom. The fusible element has one end attachedto abreech block terminal in the explosion chamber and extends out through the insulating tube to a terminal at the end'thereof. The element is "provided with a reduced section near the end attached to the breech terminal with the intent that its initial rupture shall take place within the stout explosion chamber while the insulating tube'provides the necessary insulative connection between and over a sufficient distance to prevent the are from springing between the terminals.

Due to the increase in the operating po-.

tentials of power circuits, there has been an increasing percentage of failures in the performance of this form of fuse. It has been found that when operating under heavy short circuit at high potential, the entire length of the fusible element is instantaneously converted into gas, producing an explosive action throughout the insulating tube as well as in the metal explosion chamber and resulting in the destruction of'the device. Making the tube of bigger dimensions has not proven satisfactory for the reason that while it permits of freer discharge of the large volume of gas under short circuit operation and relieves the tube of the excessive stresses, it fails snfliciently to confine the small volume of gas evolved in case of a rise in current flow just sufiicient to raisethe fusible element to its melting point, to produce the expulsive action thereon. and as a consequence an arc develops and holds through the length of the cut-out until the latter is destroyed or rendered unfunction surely and effectively under all conditions of service, which may be easily and cheaply refused and which shall be of lO\ manufacturing cost. 1

One embodiment of the invention is shown in the accompanying drawing in which:

Fig. cut-out and its mounting with parts broken; Fig. 2 is a longitudinal section of the cutout with parts broken; Fig. 3 is a perspective view of the hinged contact in which one end of the cut-out is adapted to he mounted, and Fig. 4 is a cross-section on line 14, Fig. 2.

As shown in the drawing, the cut-out comprises a metal butt 1 embodying the explosion chamber 2 and a discharge barrel in the form of a long insulating tube 3 made in two sections rigidly connected by ordinary rigid aligning brackets l. The cut-out is shown mounted in clips 5 and 6 to which the line terminals 7 and 8 are attached and each supported by a post insulator 9 of usual construction.

The metal butt 1 is bored out and threaded at its rear or lower end for the reception therein of a breech block 10 having a recess 11 in its inner'end and a round contact finger 12 at its outer end, wlnle pro ecting outwardly at its middle is a flange 13 knurled at its periphery to provide a hand hold to facilitate screwing into and out of the block 1. At the inner end of its threaded bore the butt is provided with a radial shoulder 14 against which a flange 15 of a metal cap 16 is normally pressed by the breech block 10. The upper end of the butt.1 is also bored out and threaded for attachment thereto of the adjacent section of the insulating tube 3, while an auxiliary vent aperture 17 leads out at an angle from the chamber 2 and is provided with an insulating bushing 18.

The fusible element 19 is composed of a very short section of soft fusible metal 20 of. low melting point reenforced by a wire core 21 of iron or other metal of high tensile strength and high melting point. One end of the reenforced fusible element 19 is soldered into the metal cap 16, while the opposite end is soldered into a metal shell 22.

In order that the fusible element 19 may be kept under constant and substantial tension when in use. a plunger 23 is provided with a split end 2st threaded for the recep- 1 is a side elevation of an expulsion tion of a tapered clamping thimble whereby the shell terminal 22 is mechanically and electrically connected thereto and the plunger 23 is connected by a biasing helical spring 26 to a metal block 27 secured by a screw 28 to a contact bar 29 attached by screws 30 to the upper section of the insulating tube 3. lhe contact bar 29 is provided with an eye 31 to enable it to be moved by a pole hdok (not shown) into and out of en agement with its contact clip 6. In order to protect the spring 26 from becoming impaired by heating from current passing therethrough, it is shunt circuited by a flexible copper conductor 32 connected to the adjacent ends of the plunger 23 and the metal block 27.

The lower section of the insulating tube 3, which serves as an insulating passage way for the discharge of the plunger and the gases of combustion, will vary in-length according to the potential of the circuit the cut-out is to protect and the upper section thereof will be of a length to completely house the plunger 23 when in retracted'position and entirely clear of the lower section. The space 33 between the sections affords ready escape of air and gases as the plunger moves backward and also provides a positive interruption therein so that even if the lower tube section should be carbonized and rendered conductive by the heat generated therein current Will not pass to the upper section and the parts contained therein.

When thecut-out above described operates under a heavy short circuit, the explosive action incident to the sudden volatilization of its fusible element is insuficient to disrupt or injure the enclosures since the amount, of fusible metal is very small and the arc is readily extinguished in the usual manner of expul sion fuses. lVhen the cut-out operates under a flow of current only slightly in excess of its rating. the plunger 23 is quickly retracted by its spring 26 and the are blown out by thepassage of the gases through the relatively small tube without injury thereto. The cutout, of course, under all intermediate conditions of operation functions with less chance for trouble.

' The cut-out is refused by removing from contact clips 5 and 6, unscrewing the breech block 10, dislodging the fuse cap 16,- the screw 28 disconnected and the plunger 23, spring 26 and block 2'? removed through the breech. The thimble 25 is then backed off to release the fuse shell 22 and a new fusible element with attached cap 16 and shell 2i is connected to the plunger. 23. By inserting the end of a wire in the hole 34: at the end of the block 27 and passing through the butt 1 and tube 3, the several connected parts may be drawn into position with the cap flange 15 against the breech shoulder 14, the spring 26 distended, and thescrew 28 inserted to secure the block to the contact bar 29. The breech block 10 is replaced and the cut-out is ready for use.

The contact clip carries a split bearing block 35 on a hinge pin 36 so that upon entering the finger 12 of the cut-out in the bearing block, it may be moved at its opposite end by a pole hook into engagement with the opposite contact clip 6 similar to a knifeblade switch.

l-Vhile have shown and described the best form of the invention, it do not desire to be restricted thereto.

What if claim as new and desire to secure by Letters Patent of the United States, is,-

1. An expulsion cut-out comprising an explosion chamber, an insulating passage way connected therewith, a fusible element mounted in said chamber, and a spring biased plunger connected to said fusible element and movable through and out of said passage way upon blowing of said element.

An expulsion cut-out comprising a metallic explosion chamber, an insulating tube in two discontinous sections connected therewith, a fusible element mounted in. said chamber, a plunger connected to said fusible element, biasing means for moving said plunger through the tube section adjacent said chamber, and a stationary metallic block located in the remote tubular section and connected to said biasing means.

3. An expulsion cut-out comprising an exp lgsion chamber having an internal shoulder, an insulating vent passage way connected to said chamber opposite said shoulder, a fusible element having at one end a flanged cap detachably to engage said shoulder, and an axially biased plunger detachably engaging the other end of said fusible element and located in said passage way.

4. An expulsion cut-out comprising a metallic part having an explosion chamber and a threaded recess therein, a shoulder on said metallic part between said recess and said chamber,-a breech plug provided with a con 7 tact extension at one end and a threaded extensionat the other end adapted to enter said threaded recess,.and a fusible element having a flange adapted to .be clamped between said shoulder and said contact extension. a

In witness whereof, I have hereunto set my hand this 31st, day of @ctober, 1923.

JQHN D. 1 1 ll? D, 

